darwin and modern science-第150章

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rms　of　satisfaction　or　the　reverse。

In　our　study　of　instinct　we　have　to　select　some　particular　phase　of　animal　behaviour　and　isolate　it　so　far　as　is　possible　from　the　life　of　which　it　is　a　part。　　But　the　animal　is　a　going　concern；　restlessly　active　in　many　ways。　　Many　instinctive　performances；　as　Darwin　pointed　out　（〃Origin　of　Species〃　（6th　edition）；　page　206。）；　are　serial　in　their　nature。　　But　the　whole　of　active　life　is　a　serial　and　coordinated　business。　　The　particular　instinctive　performance　is　only　an　episode　in　a　life…history；　and　every　mode　of　behaviour　is　more　or　less　closely　correlated　with　other　modes。　　This　coordination　of　behaviour　is　accompanied　by　a　correlation　of　the　modes　of　primary　experience。　　We　may　classify　the　instinctive　modes　of　behaviour　and　their　accompanying　modes　of　instinctive　experience　under　as　many　heads　as　may　be　convenient　for　our　purposes　of　interpretation；　and　label　them　instincts　of　self…preservation；　of　pugnacity；　of　acquisition；　the　reproductive　instincts；　the　parental　instincts；　and　so　forth。　　An　instinct；　in　this　sense　of　the　term　（for　example　the　parental　instinct）；　may　be　described　as　a　specialised　part　of　the　primary　tissue　of　experience　differentiated　in　relation　to　some　definite　biological　end。　　Under　such　an　instinct　will　fall　a　large　number　of　particular　and　often　well…defined　modes　of　behaviour；　each　with　its　own　peculiar　mode　of　experience。

It　is　no　doubt　exceedingly　difficult　as　a　matter　of　observation　and　of　inference　securely　based　thereon　to　distinguish　what　is　primary　from　what　is　in　part　due　to　secondary　acquisitiona　fact　which　Darwin　fully　appreciated。　　Animals　are　educable　in　different　degrees；　but　where　they　are　educable　they　begin　to　profit　by　experience　from　the　first。　　Only；　therefore；　on　the　occasion　of　the　first　instinctive　act　of　a　given　type　can　the　experience　gained　be　weighed　as　WHOLLY　primary；　all　subsequent　performance　is　liable　to　be　in　some　degree；　sometimes　more；　sometimes　less；　modified　by　the　acquired　disposition　which　the　initial　behaviour　engenders。　　But　the　early　stages　of　acquisition　are　always　along　the　lines　predetermined　by　instinctive　differentiation。　　It　is　the　task　of　comparative　psychology　to　distinguish　the　primary　tissue　of　experience　from　its　secondary　and　acquired　modifications。　　We　cannot　follow　up　the　matter　in　further　detail。　　It　must　here　suffice　to　suggest　that　this　conception　of　instinct　as　a　primary　form　of　experience　lends　itself　better　to　natural　history　treatment　than　Darwin's　conception　of　an　impelling　force；　and　that　it　is　in　line　with　the　main　trend　of　Darwin's　thought。

In　a　characteristic　work；characteristic　in　wealth　of　detail；　in　closeness　and　fidelity　of　observation；　in　breadth　of　outlook；　in　candour　and　modesty；Darwin　dealt　with　〃The　Expression　of　the　Emotions　in　Man　and　Animals〃。　　Sir　Charles　Bell　in　his　〃Anatomy　of　Expression〃　had　contended　that　many　of　man's　facial　muscles　had　been　specially　created　for　the　sole　purpose　of　being　instrumental　in　the　expression　of　his　emotions。　　Darwin　claimed　that　a　natural　explanation；　consistent　with　the　doctrine　of　evolution；　could　in　many　cases　be　given　and　would　in　other　cases　be　afforded　by　an　extension　of　the　principles　he　advocated。　　〃No　doubt；〃　he　said　（〃Expression　of　the　Emotions〃；　page　13。　　The　passage　is　here　somewhat　condensed。）；　〃as　long　as　man　and　all　other　animals　are　viewed　as　independent　creations；　an　effectual　stop　is　put　to　our　natural　desire　to　investigate　as　far　as　possible　the　causes　of　Expression。　　By　this　doctrine；　anything　and　everything　can　be　equally　well　explained。。。With　mankind；　some　expressions。。。can　hardly　be　understood；　except　on　the　belief　that　man　once　existed　in　a　much　lower　and　animal…like　condition。　　The　community　of　certain　expressions　in　distinct　though　allied　species。。。is　rendered　somewhat　more　intelligible；　if　we　believe　in　their　descent　from　a　common　progenitor。　　He　who　admits　on　general　grounds　that　the　structure　and　habits　of　all　animals　have　been　gradually　evolved；　will　look　at　the　whole　subject　of　Expression　in　a　new　and　interesting　light。〃

Darwin　relied　on　three　principles　of　explanation。　　〃The　first　of　these　principles　is；　that　movements　which　are　serviceable　in　gratifying　some　desire；　or　in　relieving　some　sensation；　if　often　repeated；　become　so　habitual　that　they　are　performed；　whether　or　not　of　any　service；　whenever　the　same　desire　or　sensation　is　felt；　even　in　a　very　weak　degree。〃　　（Ibid。　page　368。）　　The　modes　of　expression　which　fall　under　this　head　have　become　instinctive　through　the　hereditary　transmission　of　acquired　habit。　　〃As　far　as　we　can　judge；　only　a　few　expressive　movements　are　learnt　by　each　individual；　that　is；　were　consciously　and　voluntarily　performed　during　the　early　years　of　life　for　some　definite　object；　or　in　imitation　of　others；　and　then　became　habitual。　　The　far　greater　number　of　the　movements　of　expression；　and　all　the　more　important　ones；　are　innate　or　inherited；　and　such　cannot　be　said　to　depend　on　the　will　of　the　individual。　　Nevertheless；　all　those　included　under　our　first　principle　were　at　first　voluntarily　performed　for　a　definite　object；namely；　to　escape　some　danger；　to　relieve　some　distress；　or　to　gratify　some　desire。〃　　（Ibid。　pages　373；　374。）

〃Our　second　principle　is　that　of　antithesis。　　The　habit　of　voluntarily　performing　opposite　movements　under　opposite　impulses　has　become　firmly　established　in　us　by　the　practice　of　our　whole　lives。　　Hence；　if　certain　actions　have　been　regularly　performed；　in　accordance　with　our　first　principle；　under　a　certain　frame　of　mind；　there　will　be　a　strong　and　involuntary　tendency　to　the　performance　of　directly　opposite　actions；　whether　or　not　these　are　of　any　use；　under　the　excitement　of　an　opposite　frame　of　mind。〃　　（〃Expression　of　the　Emotions〃；　page　368。）　　This　principle　of　antithesis　has　not　been　widely　accepted。　　Nor　is　Darwin's　own　position　easy　to　grasp。

〃Our　third　principle；〃　he　says　（Ibid。　page　369。）；　〃is　the　direct　action　of　the　excited　nervous　system　on　the　body；　independently　of　the　will；　and　independently；　in　large　part；　of　habit。　　Experience　shows　that　nerve…force　is　generated　and　set　free　whenever　the　cerebro…spinal　system　is　excited。　　The　direction　which　this　nerve…force　follows　is　necessarily　determined　by　the　lines　of　connection　between　the　nerve…cells；　with　each　other　and　with　various　parts　of　the　body。〃

Lack　of　space　prevents　our　following　up　the　details　of　Darwin's　treatment　of　expression。　　Whether　we　accept　or　do　not　accept　his　three　principles　of　explanation　we　must　regard　his　work　as　a　masterpiece　of　descriptive　analysis；　packed　full　of　observations　possessing　lasting　value。　　For　a　further　development　of　the　subject　it　is　essential　that　the　instinctive　factors　in　expression　should　be　more　fully　distinguished　from　those　which　are　individually　acquireda　difficult　taskand　that　the　instinctive　factors　should　be　rediscussed　in　the　light　of　modern　doctrines　of　heredity；　with　a　view　to　determining　whether　Lamarckian　inheritance；　on　which　Darwin　so　largely　relied；　is　necessary　for　an　interpretation　of　the　facts。

The　whole　subject　as　Darwin　realised　is　very　complex。　　Even　the　term　〃expression〃　has　a　certain　amount　of　ambiguity。　　When　the　emotion　is　in　full　flood　the　animal　fights；　flees；　or　faints。　　Is　this　full…tide　effect　to　be　regarded　as　expression；　or　are　we　to　restrict　the　term　to　the　premonitory　or　residual　effectsthe　bared　canine　when　the　fighting　mood　is　being　roused；　the　ruffled　fur　when　reminiscent　representations　of　the　object　inducing　anger　cross　the　mind？　　Broadly　considered　both　should　be　included。　　The　activity　of　premonitory　expression　as　a　means　of　communication　was　recognised　by　Darwin；　he　might；　perhaps；　have　emphasised　it　more　strongly　in　dealing　with　the　lower　animals。　　Man　so　largely　relies　on　a　special　means　of　communication；　that　of　language；　that　he　sometimes　fails　to　realise　that　for　animals　with　their　keen　powers　of　perception；　and　dependent　as　they　are　on　such　means　of　communication；　the　more　strictly　biological　means　of　expression　are　full　of　subtle　suggestiveness。　　Many　modes　of　expression；　otherwise　useless；　are　signs　of　behaviour　that　may　be　anticipated；signs　which　stimulate　the　appropriate　attitude　of　response。